Hallucinations in Parkinson's disease - Prevalence, phenomenology and riskfactors

Hallucinations, mainly of a visual nature, are considered to affect about o ne-quarter of patients with Parkinson's disease. They are commonly viewed a s a side-effect of antiparkinsonian treatment, but other factors may be inv olved. The aim of this study was to determine the phenomenology, prevalence and risk factors of hallucinations in Parkinson's disease. Two-hundred and sixteen consecutive patients fulfilling clinical criteria for Parkinson's disease were studied. Demographic and clinical variables were recorded, inc luding motor and cognitive status, depressive symptoms and sleep-wake distu rbances. Patients with and without hallucinations were compared using non-p arametric tests, and logistic regression was applied to significant data. H allucinations had been present during the previous 3 months in 39.8% of the patients, and fell into three categories: minor forms, consisting of a sen sation of a presence (person), a sideways passage (commonly of an animal) o r illusions were present in 25.5% of the patients (an isolated occurrence i n 14.3%), formed visual hallucinations were present in 22.2% (isolated in 9 .3%) and auditory hallucinations were present in 9.7% (isolated in 2.3%), P atients with minor hallucinations had a higher depression score than non-ha llucinators but did not differ in other respects. Logistic regression analy sis identified three factors independently predictive of formed visual hall ucinations: severe cognitive disorders, daytime somnolence and a long durat ion of Parkinson's disease. These findings indicate that, when minor halluc inations are included, the total prevalence is much higher than previously reported. A simple side-effect of dopaminergic treatment is not sufficient to explain the occurrence of all visual hallucinations. The main risk facto r in treated patients is cognitive impairment, although sleep-wake cycle di sturbances, and possibly other factors related to the duration of the disea se, act as cofactors.